U.S. patent number 5,068,088 [Application Number 07/325,459] was granted by the patent office on 1991-11-26 for method and apparatus for conducting electrochemiluminescent measurements.
This patent grant is currently assigned to Igen, Inc.. Invention is credited to Lee O. Hall, Surendera K. Tyagi, Glenn Zoski.
United States Patent |
5,068,088 |
Hall , et al. |
November 26, 1991 |
Method and apparatus for conducting electrochemiluminescent
measurements
Abstract
A method and apparatus for triggering and measuring
electrochemiluminescent phenomena using a voltage waveform applied
at the voltammetric working electrode which improves the precision
and accuracy of measurements. This waveform has a decreasing scan
rate in the range of voltages for which electrochemiluminescence is
triggered and is substantially sinusoidal in shape in this range.
The waveform results from locating the reference electrode of a
potentiostat in close potential proximity to its counter electrode,
and applying a uniform scanning voltage waveform at the reference
electrode. The waveform also can be synthesized digitally,
converted to analog form, and applied directly to the working
electrode with the reference electrode in close potential proximity
to the working electrode.
Inventors: |
Hall; Lee O. (Gaithersburg,
MD), Zoski; Glenn (Rockville, MD), Tyagi; Surendera
K. (Gaithersburg, MD) |
Assignee: |
Igen, Inc. (Rockville,
MD)
|
Family
ID: |
23267969 |
Appl.
No.: |
07/325,459 |
Filed: |
March 17, 1989 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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267234 |
Nov 3, 1988 |
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Current U.S.
Class: |
422/52; 250/361C;
324/94; 327/100; 313/498 |
Current CPC
Class: |
G01N
27/48 (20130101); H03K 4/026 (20130101); G01N
21/66 (20130101) |
Current International
Class: |
G01N
27/48 (20060101); G01N 21/62 (20060101); G01N
21/66 (20060101); H03K 4/02 (20060101); H03K
4/00 (20060101); G01N 021/76 (); H01J 001/62 ();
H03K 004/00 () |
Field of
Search: |
;422/52 ;315/169.3,246
;313/498,358,505 ;250/361C ;340/781 ;350/331R,332
;328/181,178,228,261,268,186 ;307/353 ;204/231,412,DIG.9
;365/110,111,153 ;324/94,400,153.1,412 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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86/2734 |
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May 1986 |
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WO |
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89/10551 |
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Nov 1989 |
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WO |
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Other References
Y Ikariyama, et al., Biochemical and Biophysical Research Comm.,
vol. 128, No. 2, pp. 987-992, 4/30/85. .
Electrochemical Luminescence Based Homogeneous Immuno-Assay,
Biochemical and Biophysical Research Communications, Ikariyama et
al., vol. 128, No. 2, Apr. 1985, pp. 987-992..
|
Primary Examiner: Warden; Robert J.
Assistant Examiner: Santiago; Amalia L.
Attorney, Agent or Firm: Curtis, Morris and Safford
Parent Case Text
This application is a continuation-in-part of U.S. patent
application Ser. No. 267,234 filed Nov. 3, 1988, copending
herewith.
Claims
We claim:
1. Apparatus for measuring electrochemiluminescent phenomena of a
sample, comprising:
(a) cell means for holding a sample;
(b) voltage control means, including a working electrode, a counter
electrode, and a reference electrode, said working electrode being
located within said cell means so as to be exposable to said sample
for triggering electrochemiluminescence therein, said reference
electrode being located in potential proximity to said working
electrode so as to sense the voltage substantially adjacent
thereto,
said voltage control means further including means synthesizing a
controlled voltage waveform which is substantially a function of a
current induced in said sample during the triggering of
electrochemiluminescence, said voltage control means being coupled
with said reference electrode to apply said controlled voltage
waveform at the location of said reference electrode; and
(c) radiation detection means for detecting electrochemiluminescent
radiation from said sample.
2. An apparatus as in claim 1, wherein said means synthesizing a
controlled voltage waveform comprises a digital computer for
producing a control voltage waveform which is substantially a
function of the current induced in said sample during the
triggering of electrochemiluminescence; and a potentiostat having a
connector coupled with said digital computer to receive said
control voltage waveform and an output coupled with said working
electrode; said potentiostat being operative under the control of
said control voltage waveform means to apply said control voltage
waveform to said working electrode.
3. An apparatus as in claim 1, wherein said reference electrode is
incorporated within tubing through which the sample is pumped into
the cell means.
4. An apparatus as in claim 1, wherein said voltage control means
comprises a digital computer which is operative to synthesize a
controlled voltage waveform which is substantially sinusoidal in
shape in the voltage range for which electrochemiluminescence is
triggered.
5. An apparatus as in claim 1, wherein said voltage control means
comprises a digital computer which is operative to synthesize a
controlled voltage waveform which is a uniformly increasing voltage
waveform which becomes substantially flat within a portion of the
voltage range for which electrochemiluminisence is triggered.
6. An apparatus as in claim 1, wherein said means for synthesizing
a controlled voltage waveform comprises a digital computer for
synthesizing said controlled voltage waveform in digital form, and
means for converting said digital waveform to an analog
waveform.
7. A method for measuring electrochemiluminescent phenomena of a
sample, said method comprising the steps of:
(a) introducing said sample into a cell having a working electrode
located within said cell so as to be exposable to said sample;
(b) applying a controlled voltage waveform to said working
electrode to trigger electrochemiluminescence in said sample;
(c) generating said controlled voltage waveform substantially as a
function of the current induced in said sample during the
triggering of electrochemiluminescence; and
(d) detecting electrochemiluminescent radiation from said
sample.
8. A method as in claim 7, wherein the step of generating said
controlled voltage waveform comprises synthesizing said controlled
voltage waveform in digital form and converting said digital
waveform to an analog waveform.
9. A method as in claim 7, wherein the step of generating said
controlled voltage waveform comprises generating a controlled
voltage waveform which is substantially sinusoidal in shape in the
voltage range for which electrochemiluminescence is triggered.
10. A method as in claim 7, wherein the step of generating said
controlled voltage waveform comprises generating a controlled
voltage waveform which is a uniformly increasing voltage waveform
which becomes substantially flat within a portion of the voltage
range for which electrochemiluminescence is triggered
11. An apparatus for operating a working electrode in a cell
adapted to trigger electrochemiluminescence in a sample,
comprising:
(a) holding means for receiving and holding a sample;
(b) working electrode means positioned in said holding means to be
exposed to said sample; and
(c) voltage control means applying a voltage waveform to said
working electrode means to trigger electrochemiluminescence in said
sample, said waveform being substantially a function of a current
induced in said sample during said triggering.
12. An apparatus as in claim 11, wherein said voltage control means
comprises a digital computer for producing a control voltage
waveform which is substantially a function of the current induced
in said sample during the triggering of electrochemiluminescence;
and a potentiostat having a connector coupled with said digital
computer to receive said control voltage waveform and an output
coupled with said working electrode; said potentiostat being
operative under the control of said control voltage waveform means
to apply said control voltage waveform to said working
electrode.
13. An apparatus as in claim 11, further comprising a digital
computer for synthesizing said voltage waveform in digital form,
and means for converting said digital waveform to an analog
waveform.
14. An apparatus as in claim 11, further comprising:
counter electrode means positioned in said holding means to be
exposed to said sample for supplying current to said working
electrode means; and
reference electrode means positioned in said holding means to be
exposed to said sample in potential proximity to said counter
electrode means for sensing a voltage;
said voltage control means being coupled with said reference
electrode means to adjustably apply a predetermined voltage
waveformat the position thereof such that the voltage waveform at
said working electrode means corresponds to a difference between
said predetermined voltage waveform and a voltage difference
resulting from the flow of current between said counter electrode
and said working electrode.
Description
FIELD OF THE INVENTION
This invention relates to electrochemiluminescent phenomena and
more particularly to a system and method for detecting and
measuring electrochemiluminescent phenomena.
BACKGROUND OF THE INVENTION
Measurement techniques for electrochemiluminescence (ECL) derive
from electrochemistry (EC) and chemiluminescence (CL). EC deals
generally with the relation of electricity to chemical changes and
with the interconversion of chemical and electrical energy.
CL based assay or detection techniques generally comprise forming a
mixture of a sample containing an unknown amount of an analyte of
interest with a known amount of a reactant which is conjugated with
a chemiluminescent label. The mixture is incubated to allow the
labeled reactant to bind to the analyte and then is separated into
a bound and an unbound fraction. One or both fractions are caused
to luminesce by, for example, the addition of an oxidant to the
fractions. The measured level of chemiluminescence at a specific
wavelength is indicative of the amount of the bound or unbound
fraction, and one skilled in the art can determine from such
measurements the amount of analyte in the sample.
ECL detection techniques provide a sensitive and controllable
measurement of the presence and amount of an analyte of interest In
ECL, the incubated sample is exposed to a voltammetric working
electrode, i.e., an electrode to which a voltage is applied and
into which a current for a redox reaction is passed. The ECL
mixture does not react with the chemical environment alone, as does
the CL mixture, or with an electric field alone, as in EC, but
rather electrochemiluminescence is triggered by a voltage impressed
on the working electrode at a particular time and in a particular
manner to controllably cause the ECL sample to emit light at the
electrochemiluminescent wavelength of interest. The measurement is
not the current at the electrode, as in EC, but the frequency and
intensity of emitted light.
The operating conditions affecting an ECL measurement should be
controlled from sample to sample before and during each
measurement. A knowledge of these operating conditions is necessary
to provide measurement results which are reproducible within useful
limits. Because of the complexity of these conditions, however, and
because the specific nature of all the chemical changes and
reactions occurring during ECL is not completely known, there are
substantial difficulties in reaching this goal.
Employees of the present assignee, under an obligation of
assignment to it, have found that techniques which improve the
measurement of current in EC do not necessarily improve the
measurement of the frequency and intensity of light emitted during
ECL. The optimal conditions for ECL measurements must meet
different criteria.
The voltage waveform impressed upon the voltammetric electrode of
an ECL cell must be sufficient to trigger electrochemiluminescence.
This voltage waveform usually is in the form of a uniform voltage
sweep starting at a first voltage, moving steadily to a second
voltage, moving back through the first voltage to a third voltage
and then back again to the first voltage. Other waveforms have been
applied in practice, however, and can trigger ECL.
In order to be meaningful, the ECL measurement must be precise,
i.e., repeatable within strict limits with the same operating
conditions and ECL sample. The measurement also must be accurate,
i.e., within acceptable limits of the actual concentration of
analyte present in the sample. Since the ECL reaction chemically
changes the sample, only one ECL measurement generally can be taken
for each sample. These chemical changes occur predominantly within
a thin layer of the sample adjacent the working electrode.
Precision and accuracy are sensitive to, among other things, the
voltage waveform impressed upon the working electrode to trigger
electrochemiluminescence. Although an optimal waveform may exist
theoretically for a given sample and operating conditions,
achieving this waveform is difficult because of the multiplicity of
factors affecting the ECL response. The present inventors have
found, however, that certain modifications in conventional
waveforms, apparatus and techniques, which effectively diminish the
extent to which this waveform is controlled at its operative point
adjacent the working electrode, unexpectedly increase the quality
of an ECL response and the precision and accuracy of its
measurement.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method and
apparatus for improving the precision and accuracy of
electrochemiluminescent measurements.
It is another object of this invention to provide a voltage
waveform for triggering ECL which improves an ECL response and its
measurement.
It also is an object of the present invention to provide a method
and apparatus for impressing a voltage waveform on an ECL cell
which enhances the precision and accuracy of ECL measurements.
It is a further object of the present invention to provide a method
and apparatus for applying an improved waveform on an ECL cell
using a potentiostat.
It is yet another object of the present invention to provide a
method and apparatus for synthesizing a controlled voltage waveform
for application to the working electrode of an ECL cell.
In accordance with one aspect of the present invention, the uniform
scanning voltage waveform applied to the working electrode of an
ECL cell to trigger electrochemiluminesence is modified such that
the precision and accuracy of ECL measurements are improved. This
modified waveform is substantially sinusoidal in shape at the
voltages where ECL is triggered. This modification advantageously
causes the ECL reaction to slow and occur more uniformaly and
consistently and enables ECL measurements to be made more precisely
and accurately.
A conventional electrochemical or ECL cell comprises a working
electrode, a counter electrode and a reference electrode, and the
voltage waveform for triggering electrochemiluminescence is applied
to the working electrode using a potentiostat. The potentiostat
applies a controlled voltage waveform at the reference electrode,
with respect to the working electrode, and the working electrode is
maintained at virtual ground. In order that the waveform adjacent
the working electrode is known and controlled, the reference
electrode is placed in close potential proximity to the working
electrode.
In accordance with another aspect of this invention, the reference
electrode of the ECL cell is placed in close potential proximity to
the counter electrode, and a controlled voltage waveform is applied
at the reference electrode. This placement diminishes the extent to
which the waveform applied at the working electrode can be
controlled. Because of the voltage drop within the cell between the
counter and working electrodes, this waveform becomes modified at
its operative point adjacent the working electrode. The amount of
modification is substantially proportional to the resistance of the
solution in the cell and the current passing between the counter
and working electrodes. The present inventors have found that
although the solution resistance remains substantially constant
throughout an ECL event, the current in the cell increases near the
voltage where light is emitted. As a result, if the controlled
voltage waveform has a uniform scan rate, the waveform occurring at
the working electrode decreases in scan rate and is found to become
substantially sinusoidal in shape around the voltage at which ECL
occurs. This modified waveform occurring at the working electrode,
although subject to less control by the potentiostat,
advantageously results in more precise and accurate ECL
measurements.
This invention also comprises in another aspect synthesizing the
modified waveform occurring at the working electrode, when the
reference electrode is adjacent the counter electrode, and then
applying this synthesized waveform directly to the working
electrode with the reference electrode adjacent the working
electrode for more precise control. With the reference electrode in
the latter position, the operative waveform applied to the working
electrode can be accurately controlled and closely monitored by the
potentiostat.
Since the degree to which a waveform at the reference electrode
becomes modified at the working electrode is substantially a
function of the current flowing between the counter and working
electrodes, this modified waveform can be calculated from a measure
of the current flowing in the ECL cell during an ECL event. A
computer or microprocessor can be used advantageously to perform
this calculation and to synthesize the modified waveform digitally,
and the digitally synthesized waveform can be converted to an
analog waveform using an digital-to-analog converter. The
synthesized analog waveform then can be applied precisely to the
working electrode using a potentiostat with the reference electrode
in close potential proximity to the working electrode. This method
has the further advantage that small changes can be made to the
synthesized waveform and accurately evaluated for further
improvement in the ECL response and measurement.
In another aspect, this invention provides apparatus for applying a
modified scanning voltage waveform to the working electrode of an
ECL cell. This apparatus preferably comprises a potentiostat with
its reference electrode in close potential proximity to its working
electrode, and the modified waveform preferably is substantially a
function of the current induced in the ECL cell during the
triggering of electrochemiluminescence. Advantageously, the
apparatus first synthesizes the modified waveform digitally,
converts the digital waveform to an analog waveform and then
applies the analog waveform to the working electrode using the
potentiostat with its reference electrode in close potential
proximity to the working electrode.
This invention also provides in another aspect a method for
measuring electrochemiluminescent phenomena by applying a modified
scanning voltage waveform to the working electrode of an ECL cell
to trigger electrochemiluminesence with the modified voltage
waveform being substantially a function of the current induced in
the ECL cell during electrochemiluminescence. The modified voltage
waveform preferably is the result of a uniform scanning voltage
waveform (triangular waveform) minus a second waveform having a
magnitude substantially a function of the current induced in the
ECL cell.
Advantageously, this method further comprises synthesizing the
modified voltage waveform digitally, converting the digital
waveform to an analog waveform using an analog to digital converter
and then applying the analog waveform to the working electrode of
an ECL cell.
It is not intended that the invention be summarized here in its
entirety. Rather, further features, aspects and advantages of the
invention will be set forth in, or will be apparent from, the
following description and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a front view of an apparatus according to the present
invention;
FIG. 2 is a block diagram of voltage control apparatus for
controlling the voltages applied to the apparatus of FIG. 1;
FIG. 3 is a waveform diagram illustrating voltages applied to the
apparatus of FIG. 1;
FIG. 4 is a waveform diagram illustrating voltages, modified in
accordance with the present invention, for application to the
apparatus of FIG. 1; and
FIG. 5 is a block diagram of voltage control apparatus for
synthesizing and applying the voltages illustrated in FIG. 4 to the
apparatus of FIG. 1.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 shows an ECL measuring apparatus 10 for applying the present
invention. Apparatus 10 is a flow-through type ECL measuring
apparatus, but, as is apparent from the following description, this
invention is not limited to flow-through type ECL measuring
apparatus and may be employed advantageously in all types of ECL
apparatus utilizing a working electrode or other triggering surface
to provide electrochemical energy to trigger an analyte of interest
into electrochemiluminesence.
Apparatus 10 comprises an ECL cell 12, mounted on supporting
structure 42, enclosed within light-tight drawer 14 which is
removably mounted within a larger instrument for conducting ECL
measurements. This instrument also includes detecting and measuring
apparatus (not shown) for detecting and measuring the light emitted
from a sample within the ECL cell 12 during ECL. The detecting and
measuring apparatus advantageously may be a photomultiplier tube,
photodiode, charge coupled device, photographic film or the like.
For a further description of suitable detecting and measuring
apparatus, reference is made to U.S. patent application Nos.
188,258 and 187,095, assigned in common with the present
application.
Intake tubing 22, which may be constructed advantageously of
stainless steel, passes through drawer 14 into a container (not
shown) holding a solution to be sampled. A pump (also not shown),
which is advantageously a peristaltic pump, at the end of exit
tubing 24 causes a sample of this solution to pass through the
intake tubing 22 into the sample holding volume 44 of the ECL cell.
Electrochemiluminescence is triggered within the cell by working
electrode 18 and counter electrode 16 and is measured by the
detecting and measuring apparatus. After the measurement, the
sample is pumped out of the holding volume 44, through exit tubing
24 (also advantageously constructed of stainless steel), and
through the reference electrode holding volume 46. This process is
repeated for each sample to be tested.
In order to substantially duplicate operating conditions prior to
and during testing from sample to sample, various cleaning and
conditioning solutions advantageously are pumped into the ECL cell
prior to each sample. For a description of such cleaning and
conditioning solutions and techniques for their application,
reference is made to U.S. patent application No. 188,258, assigned
in common with the present application.
Reference electrode 20 is incorporated within exit tubing 24 and
enclosed within housing 28. In this position, this electrode is
exposed to substantially the same voltage potential within the
solution in sample holding volume 44 as that to which the counter
electrode 16 is exposed. If housing 28 and reference electrode 20
were incorporated within the intake tubing 22, rather than the exit
tubing 24, the reference electrode would be exposed to
substantially the same voltage potential within the sample solution
as that to which the working electrode 18 is exposed. The latter
position is that generally used in a conventional electrochemical
cell.
Connectors 32, 34 and 36 connect the reference electrode 20,
working electrode 18 and counter electrode 16, respectively, to
terminal connectors 30 which are connected to the voltage control
circuit 60 shown in FIG. 2. Male connectors 38 and 40 are removably
inserted into female connectors within supporting structure 42 to
enable the ECL cell to be electrically disassociated from the
voltage control circuit and the working and counter electrodes to
be reversed in function if desired.
Voltage control circuit 60, shown in FIG. 2, advantageously
operates in the manner of a potentiostat to supply a controlled
voltage waveform at reference electrode 20 with respect to the
working electrode 18. Connectors 62, 64 and 68 of voltage control
60 are connected to terminals 30 and then to connectors 34, 36 and
32, respectively, which are connected to the working electrode 18,
counter electrode 16 and reference electrode 20, respectively, of
ECL apparatus 10. An input voltage V.sub.in to voltage control 60
is provided on connector 70. Connector 62, connected to the working
electrode 18, and input connector 72 are held at virtual
ground.
In operation, voltage control 60 forces the voltage appearing on
connector 68, connected to the reference electrode 20, to duplicate
V.sub.in appearing on input connector 70. No significant current
flows through reference electrode 20, but this electrode provides a
reference against which the voltage between the counter and working
electrodes adjusts until the voltage at the reference electrode,
with respect to the working electrode (i.e., ground), duplicates
the voltage V.sub.in on connector 70. Potentiostats for this
purpose are well known, and the internal structure of voltage
control 60 may correspond to any of the conventional, commercially
available potentiostats which operate in this manner.
Reference electrode 20 senses a voltage potential within the sample
solution substantially equivalent to that adjacent counter
electrode 16. If reference electrode 20 were located within the
intake tubing 22 above the working electrode 18 shown in FIG. 1,
then the reference electrode would sense substantially the same
potential within the solution as that adjacent working electrode
18. The same result could be achieved by reversing male connectors
38 and 40 which would in effect make electrode 16 the working
electrode and electrode 18 the counter electrode.
Locating the reference electrode at a voltage potential
substantially equivalent to that adjacent the working electrode
enables the voltage waveform applied to the working electrode to be
precisely controlled and closely monitored. This position is
conventional for electrochemical cells.
FIG. 3 is a waveform diagram of voltages within ECL cell 12 during
the triggering of ECL with the reference electrode 20 at a position
for sensing the voltage substantially adjacent the working
electrode (a position opposite to that shown in FIG. 1). Waveform
100 is the voltage applied at the reference electrode, and waveform
102 is the voltage measured within the solution by a probe
substantially adjacent the counter electrode. The scan rate for the
applied voltage 100 is 500 millivolts per second.
These plots show that voltage control 60, with the reference
electrode and its conventional position for sensing the voltage
adjacent the working electrode, forces both waveforms to be
triangular and follow a substantially constant scan rate. At any
given time, the voltage measured adjacent the counter electrode
(waveform 102) exceeds that applied at the reference electrode
(waveform 100) because of the voltage drop in the sample solution
caused by the current between the working and counter electrodes.
Electrochemicaluminescence is triggered at a point near the peak of
both waveforms (approximately 1.4 volts applied at the reference
electrode 20) without any modification or decrease in the scan rate
during the period of ECL.
FIG. 4 is a waveform diagram of voltages within ECL cell 12 during
the triggering of ECL with the reference electrode 20 in the
alternative position shown in FIG. 1 for sensing the voltage
adjacent the counter electrode. Waveform 110 is the voltage applied
at the reference electrode, which has a uniform scan rate of 500
millivolts per second, and waveform 112 is the voltage measured
within the sample solution by a probe substantially adjacent the
working electrode. Waveform 112 shows a decrease in the scan rate
or a plateauing around the period that electrochemiluminescence
occurs. The voltage measured adjacent the working electrode during
this period is between 1.4 and 1.6 volts. The potentiostat,
however, keeps the applied voltage in the solution at the reference
electrode adjacent the counter electrode, waveform 110, at the
uniform, selected scan rate. The latter voltage exceeds the voltage
adjacent the working electrode during chemiluminescence by
approximately .8 volts because of the voltage drop between the
counter and working electrodes resulting from the cascading of
current during this period. This phenomenon keeps the voltage
adjacent the working electrode at substantially that necessary to
maintain electrochemiluminesce without overshooting this voltage
and disadvantageously accelerating the event. This result enables a
more precise and accurate electrochemiluminescent response and
measurement of data.
FIG. 5 shows a second embodiment of apparatus for control of the
voltages applied to the apparatus of FIG. 1. This second embodiment
advantageously synthesizes the waveform digitally that is applied
at the reference electrode, with respect to the working electrode,
using digital computer 120. This digitally synthesized waveform
advantageously is equivalent to waveform 112, the waveform
resulting at the working electrode with the reference electrode in
its alternative position adjacent the counter electrode, when the
waveform applied at the reference electrode is a uniform scanning
voltage waveform. This synthesized waveform is applied to ECL cell
12 with reference electrode 20 in its conventional position
adjacent working electrode 18. The digital synthesization of the
waveform also can be effected with a microprocessor, special
purpose computer or similar digital device.
Since the potential drop between the counter and working electrodes
is primarily a function of the current flowing between these
electrodes, the digitally synthesized waveform can be calculated
from a measure of the current flowing in the ECL cell during ECL
with the reference electrode in its alternative position adjacent
the counter electrode. This current times the resistance of the
sample solution defines a second waveform which is subtracted from
the uniform scanning voltage waveform (triangular waveform) applied
at the reference electrode to create the modified waveform.
The digitally synthesized waveform is fed through data lines 126 to
digital to analog converter 122 whose output on connector 128, with
respect to that appearing on connector 130 which is held at virtual
ground, is the corresponding synthesized waveform in analog form.
The voltage appearing on connector 128 is the input voltage
V.sub.in to voltage control 124 which, like voltage control 60,
advantageously operates in the manner of a potentiostat to supply a
controlled voltage waveform substantially identical to V.sub.in on
connector 136 with respect to connector 132 (virtual ground). In
this embodiment, reference electrode 20 is located within the
intake tubing 22 (opposite to the position shown in FIG. 1) for
sensing the voltage potential within the sample solution
substantially equivalent to that surrounding working electrode 18.
Connectors 132, 134 and 136 of voltage control 124 are connected
through terminals 30 to connectors 34, 36 and 32, respectively,
and, therefore, to the working electrode 18, counter electrode 16
and reference electrode 20, respectively, of ECL apparatus 10.
In this embodiment, the applied scanning waveform is synthesized
with its desirable plateau and substantially sinusoidial shape
around the voltage for triggering ECL, and this waveform is
precisely applied directly to the working electrode. This
embodiment also enables minor modifications to be made in the
synthesized waveform, and the degree to which they improve or
adversely affect ECL response and measurements, to be directly
correlated.
Although embodiments of the present invention have been described
in detail herein with reference to the accompanying drawings, it is
apparent that the invention is not limited to these embodiments and
drawings and that various changes and modifications may be effected
by one skilled in the art without departing from the spirit and
scope of the invention as defined in the following claims.
* * * * *